Driving assistance device and driving assistance program product

ABSTRACT

A driving assistance device includes: a risk degree obtaining portion obtaining a degree of a risk of an event threatening a safety of a driver when an occurrence of the event is predicted; a risk handling control portion controlling an execution of a risk handling measure by a risk handling unit against the event that is predicted; a risk factor obtaining portion obtaining a factor which causes the risk as a risk factor; and a presentation control portion controlling a presentation of information about the risk factor. The presentation control portion presents information indicating a presence of the risk factor when the risk handling control portion controls the risk handling unit not to execute the risk handling measure and the degree of the risk is equal to or higher than a predetermined value.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation Application of U.S. patentapplication Ser. No. 16/089,242 filed Sep. 27, 2018 which is a U.S.National Phase Application under 35 U.S.C. 371 of InternationalApplication No. PCT/JP2017/009958 filed on Mar. 13, 2017. Theseapplications are based on and claim the benefit of priority fromJapanese Patent Application No. 2016-074381 filed on Apr. 1, 2016. Theentire disclosures of all of the above applications are incorporatedherein by reference.

TECHNICAL FIELD

The present disclosure relates to a driving assistance device and to adriving assistance program product.

BACKGROUND ART

It is important for safety that a driver's line of sight is directed toa road in a vehicle moving direction while driving. A driving assistanceconfiguration proposed in the related art presents warning informationindicating an occurrence of an event threatening safety of a driver (forexample, appearance of a bicycle running parallel to an own vehicle)upon occurrence of such an event (see, for example, Patent Literature1).

PRIOR ART LITERATURE Patent Literature

-   Patent Literature 1: JP 2015-106326 A

SUMMARY OF INVENTION

An occurrence of an event threatening safety of the driver is aprecondition for the configuration of the above-described related artand warning information is presented after the event becomes apparent.The configuration above is effective in giving warning to the driver.However, the driver is unable to take any measure unless the eventthreatening safety of the driver becomes apparent. A well-experienceddriver knows tips on where to look to drive safely and has a habit ofsafe driving whereas an inexperienced driver is less likely to know suchtips and have a habit of safe driving.

In view of the foregoing difficulties, it is an object of the presentdisclosure to provide a driving assistance device and a drivingassistance program product capable of properly assisting a driver withdriving operation by giving a driver tips on where to look to drivesafely.

According to an aspect of the present disclosure, a risk degreeobtaining portion obtaining a degree of a risk of an event threatening asafety of a driver when an occurrence of the event is predicted; a riskhandling control portion controlling an execution of a risk handlingmeasure by a risk handling unit against the event that is predicted; arisk factor obtaining portion obtaining a factor which causes the riskas a risk factor; and a presentation control portion controlling apresentation of information about the risk factor. The presentationcontrol portion presents information indicating a presence of the riskfactor when the risk handling control portion controls the risk handlingunit not to execute the risk handling measure and the degree of the riskis equal to or higher than a predetermined value.

Information indicating presence of a risk factor is presented when adegree of risk becomes equal to or above the predetermined value evenwhen the risk handling unit does not take a risk handling measure sincean event threatening safety of the driver is not apparent. By presentinginformation indicating presence of a risk factor before an eventthreatening safety of the driver becomes apparent, the drivingassistance device can control a driver's line of sight to direct to adirection in which the risk factor is present. The configuration asabove is thus capable of appropriately assisting a driver with drivingoperation by giving the driver tips on where to look to drive safely.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

FIG. 1 is a functional block diagram of one embodiment;

FIG. 2 is a diagram showing a flowchart of a process performed by alogical formula conversion portion;

FIG. 3A shows a table indicating a relationship between an objectrecognition result and a logical constant;

FIG. 3B shows tables indicating conversion rules applied when convertingobservation information into a logical formula;

FIG. 4 shows a table indicating how costs are assigned to observationliterals;

FIG. 5 shows a table indicating an intention estimation knowledge base;

FIG. 6 shows a table indicating a natural law knowledge base;

FIG. 7 shows a table indicating a risk factor knowledge base;

FIG. 8 shows a flowchart of a process performed by an abductiveinference portion;

FIG. 9 shows a flowchart of a process performed by a control unit;

FIG. 10 is a diagram showing a display example when a risk factor ispresented; and

FIG. 11 is a diagram showing a display example when a risk factor is notpresented.

EMBODIMENTS FOR CARRYING OUT INVENTION

Hereinafter, one embodiment will be described with reference to thedrawings. A driving assistance system 1 includes a driving assistancedevice 2, an observation information obtaining unit 3, a risk handlingunit 4, and an information presentation system 5.

The observation information obtaining unit 3 includes an image sensor 6,a laser sensor 7, a navigation system 8, a vehicle state sensor group 9,a road-to-vehicle communication device 10, and a vehicle-to-vehiclecommunication device 11. The image sensor 6 and the laser sensor 7obtain information on various objects present on a periphery of avehicle. The navigation system 8 detects a present location of thevehicle and obtains various types of information from a map near thepresent location. The vehicle state sensor group 9 obtains informationon a behavior of the vehicle and a state of the vehicle. Theroad-to-vehicle communication device 10 obtains information on trafficjamming, road regulations, and so on from a communication party which isprovided by an infrastructure. The vehicle-to-vehicle communicationdevice 11 obtains information on a behavior of another vehicle presenton the periphery of the vehicle. The observation information obtainingunit 3 observes a situation of the vehicle and surrounding circumstancesof the vehicle from the information specified above, generates anobservation information group D1 for an object present on the peripheryof the vehicle, and outputs the observation information group D1 thusgenerated to the driving assistance device 2. The observationinformation group D1 generated in the observation information obtainingunit 3 contains information on at least a type of object, an attributeof object, and information reliability. For example, in a case where anobject is a mobile object, an attribute of object includes a location, amoving velocity, and a moving direction of the object, and so on. In acase where an object is a pedestrian, an attribute of object may includea gender, an adult or a child, belongings, and so on.

Upon input of a risk handling signal from the driving assistance device2, the risk handling unit 4 takes a risk handling measure, such ascontrols the vehicle and notifies the driver of a risk. The riskhandling unit 4 controls the vehicle by taking a risk handling measure,for example, a speed control, a speed reduction, an emergency stop, andautomated driving to avoid a risk. The risk handling unit 4 notifies thedriver of a risk by taking a risk handling measure, such as an auditorynotification or a visual notification. The risk handling unit 4 providesan auditory notification by, for example, outputting a warning soundfrom a buzzer, outputting a warning speech as an audio guidance from aspeaker. The risk handling unit 4 provides a visual notification by, forexample, displaying a danger spot on a map screen, displaying a dangerspot and attracting the driver's line of sight to the danger spot usinga head-up display. The risk handling unit 4 may change contents of arisk handling measure depending on a degree of risk.

The information presentation system 5 is a display unit formed of, forexample, a liquid crystal display and provided to a position easy to seefrom the driver even while driving, such as close to a speedometer. Uponinput of a presentation command signal from the driving assistancedevice 2, the information presentation system 5 presents (displays) arisk factor which may develop to a risk. A risk factor may be a bicyclerunning parallel to an own vehicle, a pedestrian walking along aroadside, another vehicle coming closer to the own vehicle in an attemptto overtake. The risk factor is an event threatening safety of thedriver.

The driving assistance device 2 includes a control unit 12 and aknowledge base 13. The control unit 12 is formed of a micro-computerhaving a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM(Random Access Memory), and an I-O (Input-Output). By running a computerprogram stored in a non-transitory tangible recording medium, thecontrol unit 12 performs a process according to the computer program andcontrols an overall operation of the driving assistance device 2. Thecomputer program executed by the control unit 12 includes a drivingassistance program.

The control unit 12 includes a logical formula conversion portion 12 a,an abductive inference portion 12 b, an inference result interpretationportion 12 c, a risk degree obtaining portion 12 d, a risk handlingcontrol portion 12 e, a risk factor obtaining portion 12 f, and apresentation control portion 12 g. The respective portions 12 a through12 g are formed of the computer program executed by the control unit 12and implemented in software manner.

The logical formula conversion portion 12 a converts the observationinformation group D1 generated in the observation information obtainingunit 3 into a logical formula. Hereinafter, a literal forming a logicalformula is expressed as Li, where i is an identifier and has a value ofpositive integer. A literal means a logical formula without a partiallogical formula. A cost is given to each literal. A cost is a value setaccording to reliability of a literal and hence reliability ofobservation, which is a literal generation source, and expressed as ci.Herein, a cost ci is set to a value ranging from 1 to 100 in inverseproportion to reliability. That is, a cost ci=1 means that a contentexpressed by a literal Li definitely holds true and means 100%reliability. Conversely, a cost ci=100 means that whether a contentexpressed by a literal Li holds true is totally unknown and means 0%reliability. Hereinafter, a literal with a cost is expressed as Li$ci.

A process performed by the logical formula conversion portion 12 a willnow be described with reference to FIG. 2.

The logical formula conversion portion 12 a assigns identification namesfor identifying objects to respective pieces of the observationinformation forming the observation information group D1 and generatesan observation information group D11 with the identification names (S1).As is set forth in FIG. 3A, logical constants represented by symbols,such as alphabets, are used as the identification names for identifyingthe objects.

The logical formula conversion portion 12 a scans the observationinformation forming the observation information group D11 withidentification names, checks the observation information against aconversion rule 21, and converts the observation information intoliterals Li. Then, the logical formula conversion portion 12 a sets acost of each literal Li to a unique value of ci=1. The logical formulaconversion portion 12 a generates an observation logical formula D12,which is a logical formula formulated by combining the literals withcosts by using a logical operator AND ({circumflex over ( )}) (S2).

As is set forth in FIG. 3B, examples of the conversion rule 21 includebut not limited to a rule relating to weather and road conditions (it israining/it is night-time/a road has an intersection), a rule relating tothe attribute of object (an object X is a car/an object Y is apedestrian/an object Y is with an open umbrella), a rule relating to apositional relationship between objects (Y is ahead of X/Y is on anintersection C/Y is closer to an intersection C than X).

As is set forth in FIG. 4, the logical formula conversion portion 12 aadjusts the cost ci for each literal with cost Li$ci, which forms theobservation logical formula D12, according to reliability of recognitionof the observation information, which is the literal generation source,and outputs an adjustment result as an observation logical formula D2with cost (S3).

The knowledge base 13 is general knowledge expressed by knowledgelogical formulae and includes an intention estimation knowledge base 13a, a natural law knowledge base 13 b, and a risk factor knowledge base13 c. Define Aj and C as literals, and define wj as a real-valued weightof a literal Aj and wj is set to 0 or greater. Then contents of therespective knowledge bases 13 a through 13 c are expressed by aknowledge logical formula (1) as follows:

A1^(w1{circumflex over ( )}) A2^(w2) {circumflex over ( )}−{circumflexover ( )}An ^(wn) →C  (1)

The intention estimation knowledge base 13 a is a description aboutrelationships among a driver's intention, a vehicle state and roadenvironment, a positional relationship with respect to a detectedobject, and so on. The intention estimation knowledge base 13 a iswritten in a predicate logic. As is set forth in FIG. 5, contents, forexample, “when a driver has an intention to turn left (right), thedriver also has an intention to slow down”, “when a left tail light isON, a driver has an intention to turn left”, and “when a heavy vehicleis running ahead, a driver may take an avoiding action” are expressed byknowledge logical formulae.

The natural law knowledge base 13 b is a description about inconsistentrelationships in physical law and concept, relationships betweenobjects, and so on. As is set forth in FIG. 6, contents, for example, “anature of being an adult and a nature of being a child are notestablished at the same time”, “a car cannot belong to different lanesat the same time”, and “a child follows a soccer ball” are expressed byknowledge logical formulae.

The risk factor knowledge base 13 c is a description about patterns ofdangerous surrounding circumstances and expressed by knowledge logicalformulae with a consequent of “risk”. As is set forth in FIG. 7,contents, for example, “in case an object exists at your location infuture, the object poses a risk”, “in a case where an object having anintention to slow down and turn left is running ahead of you, the objectposes a risk”, “in case an object invisible to you rushes out, theobject poses a risk” are expressed by knowledge logical formulae.

Knowledge logical formulae stored in the knowledge base 13 may beformulated manually or automatically obtained from web pages, a databaseof a collection of accidents, or the like by using a known text miningtechnique. A weight wj may be added to a literal Aj manually orautomatically by using a known supervised machine learning method (forexample, Fuuto Yamamoto, Naoya Inoue, Yotaro Watanabe, Naomi Okazaki,and Kentaro Inui, “Backpropagation Learning for Weighted Abduction”,Journal of Information Processing Society of Japan, Vol. 2012-NL-206,May 2012).

The following lists examples of literals converted from the observationinformation group D1 and literals used to describe contents (logicalformulae) in the knowledge base 13. Literals include literals expressingtypes of object, literals expressing states of object, literalsexpressing intentions of agents, literals expressing positionalrelationships between objects, literals expressing semanticrelationships between objects, literals expressing road conditions, andso on.

Examples of literals expressing types of object include but not limitedto: adult, agent, dangerous-agent, dog, elder, child, children, person,group-of-children, group-of-persons, ambulance, bicycle, bus, car,group-of-cars, motor-bicycle, motor-cycle, tank-truck, taxi, van,vehicle, alley, apartment, break, building, bridge, cone, gate, park,wall, cross-road, cross-walk, curve, descent, lane, intersection,railroad-crossing, signal, singal4walker, safety-zone, dangerous-spot,biscuit, soccer-ball, thing, iron-plate, leaf, light, load, obstacle,screen, puddle, and sandy-spot.

Examples of literals expressing states of object include but not limitedto: left-head-lamp-on, left-tail-light-on, right-head-lamp-on,right-tail-light-on, being-parked, empty, signal-blue,signal-blue-blink, signal-yellow, nothing-on, parked, invisible-to,visible-to, waving-hands, and wheel-drop.

Examples of literals expressing intentions of agents include but notlimited to: will-across, will-avoid, will-be-out-of-lane,will-change-direction, will-change-lane, will-cross, will-give-way,will-go-back, will-go-front, will-go-left, will-go-right,will-move-front-side, will-open-door, will-open-left-door,will-overtake, will-rush-out, will-slow-down, will-speed-up,will-splash, will-stay, and will-stop.

Examples of literals expressing positional relationships between objectsinclude but not limited to: around, behind, left-behind, left-front-of,left-of, not-in-front-of, not-left-front-of, not-left-of, right-behind,right-front-of, right-of, side-front-of, front-side-of, in-between,in-front-of, is-closer-to, is-closest-vehicle-to, on, catch, andcontact.

Examples of literals expressing semantic relationships between objectsinclude but not limited to: belongs-to, has, keep, mother-of, plays-at,follows, ride-on, and heavier-than.

Examples of literals expressing road conditions include but not limitedto: environment, facility, construction-site, rainy, wet, icy, muddy,dark, snowy, and straight.

The abductive inference portion 12 b performs an abductive inferenceabout dangerous circumstances by using the observation logical formulaD2 converted in the logical formula conversion portion 12 a and aknowledge logical formula D3 stored in the knowledge base 13. Theabductive inference portion 12 b proves a risk predicted from theobservation logical formula D2 by using the knowledge logical formula D3as background knowledge. Herein, a proof of maximum-likelihood is foundby using weighted abductive inference (see Hobbs, Jerry R., MarkStickel, Douglas AppeIt, and Paul Martin, 1993. “Interpretation asAbduction”, Artificial Intelligence, Vol. 63, Nos. 1-2, pp. 69-142).

A process performed by the abductive inference portion 12 b will now bedescribed with reference to FIG. 8.

The abductive inference portion 12 b generates a proof candidate, whichis a logical formula formulated by combining the observation logicalformula D2 and a literal expressing “risk” with a logical operator “AND(A)” and generates multiple proof candidates by applying backwardinference to the generated proof candidate (S11).

More specifically, the abductive inference portion 12 b generatesmultiple proof candidates by applying rules of the risk factor knowledgebase 13 c to a literal expressing “risk” in the proof candidategenerated first. The phrase, “apply rules”, referred to herein means aprocedure as follows. That is, define a literal forming the proofcandidate as a target literal, then the knowledge logical formula D3with the target literal as a consequent of the rule are extracted andthe target literal in the proof candidate is replaced by an antecedentof the extracted knowledge logical formula D3. The abductive inferenceportion 12 b generates a series of multiple proof candidates byrepeatedly performing the procedure to apply rules of the intentionestimation knowledge base 13 a and the natural law knowledge base 13 bto an arbitrary literal in each of the multiple proof candidatesgenerated in the manner as above. Hereinafter, a set of proof candidatesthus generated is referred to as a proof candidate group D21.

The abductive inference portion 12 b calculates a proof cost for eachproof candidate belonging to the proof candidate group D21 to select acost-lowest proof, which is a proof candidate with a most low proof cost(extract a proof of maximum-likelihood), and outputs a logical formulaand a proof cost of the cost-lowest proof as cost-lowest proofinformation D4 (S12).

The abductive inference portion 12 b calculates a proof cost by addingup costs of all literals forming the proof candidate. In a case where“rules are applied”, the abductive inference portion 12 b multiplies acost ci of a literal before replacement (literal subject to replacement)by a weight wj given to a literal after replacement (replaced literal)and uses a resulting product as a cost of the replaced literal. Forexample, when two literals of a same predicate are in the proofcandidate, the abductive inference portion 12 b unifies the two literalsby deleting whichever has the higher cost. That is, a proof costnormally increases by applying rules because the number of literalsforming the proof candidate increases. However, when same literals arein one proof candidate, the proof cost is reduced in some case. Theabove indicates that of all the rules of the risk factor knowledge base13 c, one rule that can be proved intuitively by using more observationlogical formulae is the proof of maximum likelihood.

Given that a set B of the knowledge logical formulae D3, which are rulesused for proof, and a set 0 of literals forming the observation logicalformula are expressed, respectively, by formula (2) and formula (3)below, where p(x), q(x), r(x), and s(x) are literals.

B={p(x)^(1.2) →q(x)·(x)^(0.8) {circumflex over ( )}r(x)^(0.4)→s(x)}  (2)

O={q(a)^($10) ,s(b)^($10)}  (3)

As is expressed in the formula (4) below, an observation logical formulaitself is given as a proof candidate H1. Then, a proof cost of the proofcandidate H1, cost (H1), is found in accordance with formula (5) below.

H1={q(a)^($10) ,s(b)^($10)}  (4)

cost(H1)=10+10=20  (5)

By applying a rule to a literal q(a) belonging to the proof candidateH1, a proof candidate H2 expressed by formula (6) below is generated.Deleting the literal subject to replacement from the proof candidate H2is expressed by setting a cost of the literal to $0. A proof cost of theproof candidate H2, cost (H2), is found in accordance with formula (7)below. It is understood that the proof cost of the proof candidate H2increases from the proof cost of the proof candidate H1 by applying therule, that is, by performing backward inference.

H2={q(a)^($0) ,s(b)^($10) ,p(a)^($1.2·10=$12)}  (6)

cost(H2)=10+12=22  (7)

By applying the rule to a literal s(b) belonging to the proof candidateH2, a proof candidate H3 expressed by formula (8) below is generated. Asimply found proof cost of the proof candidate H3, cost (H3), isexpressed by formula (9) below.

H3={q(a)^($0) ,s(b)^($0) ,p(a)^($12) .p(b)^($8) ,r(b)^($4)}  (8)

cost(H3)=12+8+4=24  (9)

However, same literals p(a) and p(b) are in the proof candidate H3.Hence, the two literals are unified (a=b) and the literal p(a) with thehigher cost is deleted. Consequently, the proof candidate H3 isexpressed by formula (10) below. That is, it is understood that theproof cost of the proof candidate H3, cost(H3), is actually found inaccordance with formula (11) below and that the proof cost is reduced byunifying the literals.

H3={q(a)^($0) ,s(b)^($0) ,p(b)^($8) ,r(b)^($4) ,a=b}  (10),

cost(H3)=8+4=12  (11)

The inference result interpretation portion 12 c identifies a riskpredicted from present surrounding circumstances by using thecost-lowest proof information D4 and by referring to the observationlogical formula D2 and the observation information correlated with therespective literals forming the observation logical formula D2. Theinference result interpretation portion 12 c calculates a degree of riskof the identified risk and identifies a danger spot. The inferenceresult interpretation portion 12 c is capable of identifying a risk fromthe rule of the risk factor knowledge base 13 c used to generate thecost-lowest proof and capable of calculating a degree of risk from theproof cost. To be more exact, a reciprocal of the proof cost may becalculated as a degree of risk. Alternatively, a degree of risk may becalculated by using a regression model using a proof result, proof cost,an own vehicle speed, and so on as a feature amount. Also, a danger spotmay be identified by correlating literals forming the cost-lowest proofwith identification names assigned to literals forming the observationlogical formula D2 and by using location information of an objectspecified by the observation information identified via a correlatedidentification name.

The risk degree obtaining portion 12 d obtains a degree of riskcalculated in the inference result interpretation portion 12 c. The riskhandling control portion 12 e controls the risk handling unit 4 to takea risk handling measure, such as controlling the vehicle and notifyingthe driver of a risk, as described above by using a risk predictionresult. The risk factor obtaining portion 12 f obtains a risk factorwhich may cause a risk. The presentation control portion 12 g controlspresentation of information on a risk factor by controlling an output ofa presentation command signal to the information presentation system 5.

A function of the configuration above will now be described withreference to FIG. 9 through FIG. 11.

The control unit 12 performs risk factor presentation process. Thecontrol unit 12 starts the risk factor presentation process when a startcondition of the risk factor presentation process is satisfied, forexample, when an ignition switch is switched ON from OFF. The controlunit 12 may determine that the start condition of the risk factorpresentation process is also satisfied when, for example, a vehiclespeed rises to and stays at or above a certain speed or the driver makesa predetermined operation in addition to ON-OFF switching of theignition switch.

When the risk factor presentation process starts, the control unit 12determines whether the inference result interpretation portion 12 cidentifies a risk predicted from present surrounding circumstances(S21). When it is determined that the inference result interpretationportion 12 c identifies a risk predicted from present surroundingcircumstances (S21: YES), the control unit 12 obtains a degree of riskby using the risk degree obtaining portion 12 d (S22, corresponding to arisk degree obtaining step), and determines whether the risk handlingunit 4 executes a risk handling measure (S23). When it is determinedthat the risk handling unit 4 executes a risk handling measure (S23:YES), the control unit 12 determines that an event threatening safety ofthe driver is now apparent and determines whether an end condition ofthe risk factor presentation process is satisfied (S28) by skippingSteps S24 through S27 described below.

Meanwhile, when it is determined that the risk handling unit 4 does notexecute a risk handling measure (S23: NO), the control unit 12determines that an event threatening safety of the driver is notapparent and determines whether a degree of risk is equal to or higherthan a predetermined value (S24). The control unit 12 determines whethera degree of risk is equal to or higher than the predetermined value byusing, for example, a distance between an object which configures anevent threatening safety of the driver and the own vehicle or a movingdirection of the object. For example, when it is determined that adistance between the object and the own vehicle is shorter than apredetermined distance or the object is moving in a direction to comecloser to the own vehicle, the control unit 12 determines that a degreeof risk is equal to or higher than the predetermined value. When it isdetermined that a risk of degree is equal to or higher than thepredetermined value (S24: YES), the control unit 12 obtains a riskfactor by using the risk factor obtaining portion 12 f (S25,corresponding to a risk factor obtaining step), and controls theinformation presentation system 5 to present information indicatingpresence of a risk factor by outputting a presentation command signal tothe information presentation system 5 (S26, corresponding to apresentation control step).

Meanwhile, when it is determined that, for example, a distance betweenthe object and the own vehicle is equal to or longer than thepredetermined distance or the object is moving in a direction to moveaway from the own vehicle, the control unit 12 determines that a degreeof risk is lower than the predetermined value. When it is determinedthat a degree of risk is lower than the predetermined value (S24: NO),the control unit 12 does not obtain a risk factor by using the riskfactor obtaining portion 12 f and controls the information presentationsystem 5 to present information indicating absence of a risk factor byoutputting a presentation command signal to the information presentationsystem 5 (S27, corresponding to the presentation control step).

The control unit 12 determines whether an end condition of the riskfactor presentation process is satisfied (S28). When it is determinedthat the end condition of the risk factor presentation process is notsatisfied (S28: NO), the flow returns to Step S21 to repeat Step S21 andthe following steps. When it is determined that the end condition of therisk factor presentation process is satisfied (S28: YES), for example,when the ignition switch is switched OFF from ON, the control unit 12ends the risk factor presentation process. The control unit 12 maydetermine that the end condition of the risk factor presentation processis also satisfied when a vehicle speed decreases and stays below acertain speed, or the driver makes a predetermined operation in additionto ON-OFF switching of the ignition switch.

When it is determined that the risk handling unit 4 does not execute arisk handling measure and a degree of risk is equal to or higher thanthe predetermined value, the control unit 12 determines that apossibility that an event threatening safety of the driver becomesapparent is relatively high, and presents information indicatingpresence of a risk factor as is shown in FIG. 10. In an example of FIG.10, the control unit 12 presents an icon M representing the own vehicle,an icon B representing a bicycle as a risk factor, an icon A1representing a direction in which the bicycle as the risk factor ispresent when viewed from the own vehicle, and an icon A2 representing amoving direction of the own vehicle. Accordingly, the driver is notifiedof that a bicycle as a risk factor appears ahead of the own vehicle onthe left after a short time (for example, several seconds later) beforethe bicycle actually appears ahead of the own vehicle on the left.Consequently, the driver becomes able to regularly direct the line ofsight to a left front of the vehicle and hence becomes able to drive thevehicle carefully while moving the line of sight to the left front ofthe vehicle.

When it is determined that the risk handling unit 4 does not execute arisk handling measure and a degree of risk is lower than thepredetermined value, the control unit 12 determines that a possibilitythat an event threatening safety of the driver becomes apparent isrelatively low. Hence, as is shown in FIG. 11, the control unit 12presents information indicating absence of a risk factor. In an exampleof FIG. 11, the control unit 12 presents an icon M representing the ownvehicle but does not present an icon representing a risk factor, an iconrepresenting a direction in which the risk factor is present when viewedfrom the own vehicle, or an icon representing a moving direction of theown vehicle. Accordingly, the driver is notified of that a risk factordoes not appear for a while (for example, for several seconds).Consequently, the driver's line of sight can be kept directed to avehicle moving direction and therefore the driver becomes able to drivewithout moving the line of sight unnecessarily. While the above hasdescribed examples where a bicycle running parallel to the own vehicleis a risk factor, a risk factor may be a pedestrian walking along aroadside, another vehicle coming closer to the own vehicle in an attemptto overtake, and so on. In such a case, too, the control unit 12presents information indicating presence of a risk factor in the samemanner as above.

The following advantages can be obtained by the present embodimentdescribed above.

The driving assistance device 2 presents information indicating presenceof a risk factor while a degree of risk is equal to or higher than thepredetermined value even though the risk handling unit 4 does notexecute a risk handling measure, that is, when an event threateningsafety of the driver is not apparent. By presenting informationindicating presence of a risk factor before an event threatening safetyof the driver becomes apparent, the driver's line of sight can bedirected to a direction in which the risk factor is present. The drivingassistance device 2 is thus capable of appropriately assisting a driverwith driving operation by giving the driver tips on where to look todrive safely.

The driving assistance device 2 presents information indicating absenceof a risk factor while a degree of risk is lower than the predeterminedvalue. Consequently, by presenting information indicating absence of arisk factor, the driver's line of sight can be kept directed to avehicle moving direction. Hence, an unwanted situation that the drivermoves the line of sight unnecessarily can be avoided.

While the disclosure has been described with reference to a preferredembodiment thereof, it is to be understood that the disclosure is notlimited to the preferred embodiment and constructions. The disclosure isintended to cover various modification and equivalent arrangements. Inaddition, the various combinations and configurations, which arepreferred, other combinations and configurations, including more, lessor only a single element, are also within the spirit and scope of thedisclosure.

The above has described a configuration to present informationindicating absence of a risk factor when it is determined that the riskhandling unit 4 does not execute a risk handling measure and a degree ofrisk is lower than the predetermined value as an example. Alternatively,information indicating absence of a risk factor may not be presentedwhen it is determined that the risk handling unit 4 does not execute arisk handling measure and a degree of risk is lower than thepredetermined value.

A determination as to whether a degree of risk is equal to or higherthan the predetermined value may be made continuously after theinformation indicating presence of a risk factor is presented. In such acase, presentation of the information being presented may be continuedwhen a degree of risk maintains equal to or higher than thepredetermined value and the information being presented may be erasedwhen a degree of risk decreases to a value lower than the predeterminedvalue.

In a case where multiple events with relatively high possibilities ofbecoming apparent occur at a same time, multiple icons representing therespective risk factors may be presented at the same time. For example,different icons may be presented at the same time at, for example, theright front of the vehicle and the left front of the vehicle. Whenconfigured in such a manner, the driver's line of sight can be directedregularly to the right front of the vehicle and the left front of thevehicle in turn. Hence, the driver becomes able to drive carefully bydirecting the line of sight to the right front of the vehicle and theleft front of the vehicle in turn. In a case where multiple iconsrepresenting multiple risk factors are presented at the same time, highand low degrees of risk may be presented in a distinguishable manner.For example, an icon representing a risk factor at a relatively highdegree of risk may be presented in red and an icon representing a riskfactor at a relatively low degree of risk may be presented in yellow.

What is claimed is:
 1. A driving assistance device for use in a subjectvehicle, the driving assistance device comprising: a risk degreeobtaining portion obtaining a degree of a risk of an event threatening asafety of a driver of the subject vehicle when an occurrence of theevent is predicted; a risk handling control portion controlling anexecution of a risk handling measure by a risk handling unit against theevent that is predicted; a risk factor obtaining portion obtaining afactor which causes the risk as a risk factor; and a presentationcontrol portion controlling a presentation of information about the riskfactor, wherein the presentation control portion is configured topresent, as information indicating a presence of the risk factor, (i) anicon representing the subject vehicle, (ii) an icon representing therisk factor, and (iii) an icon representing a direction in which therisk factor is present, the information indicating the presence of therisk factor includes the icon representing the subject vehicle using abird's eye view image captured from a viewpoint positioned rear andabove the subject vehicle; the information indicating the present of therisk factor includes a predetermined region that displays (i) the iconrepresenting the risk factor on front and lateral side of the iconrepresenting the subject vehicle and (ii) the icon representing thedirection in which the risk factor is present from a viewpoint of thesubject vehicle, and when the risk handling control portion controls therisk handling unit not to execute the risk handling measure and thedegree of the risk is equal to or higher than a predetermined value, thepresentation control portion presents, as the information indicating thepresence of the risk factor, (i) the icon representing the subjectvehicle, (ii) the icon representing the risk factor, and (iii) the iconrepresenting the direction in which the risk factor is present betweenthe icon representing the subject vehicle and the icon representing therisk factor.
 2. A driving assistance device for use in a subjectvehicle, the driving assistance device comprising: a risk handlingcontrol portion controlling an execution of a risk handling measure by arisk handling unit when an occurrence of an event threatening a safetyof a driver of the subject vehicle is predicted; a risk factor obtainingportion obtaining a factor which causes the risk as a risk factor; and apresentation control portion controlling a presentation of informationabout the risk factor, wherein the presentation control portion isconfigured to present, as information indicating a presence of the riskfactor, (i) an icon representing the subject vehicle, (ii) an iconrepresenting the risk factor, and (iii) an icon representing a directionin which the risk factor is present, the information indicating thepresence of the risk factor includes the icon representing the subjectvehicle using a bird's eye view image captured from a viewpointpositioned rear and above the subject vehicle; the informationindicating the present of the risk factor includes a predeterminedregion that displays (i) the icon representing the risk factor on frontand lateral side of the icon representing the subject vehicle and (ii)the icon representing the direction in which the risk factor is presentfrom a viewpoint of the subject vehicle, and when the risk handlingcontrol portion controls the risk handling unit not to execute the riskhandling measure and the risk factor is determined to be existing, thepresentation control portion presents, as the information indicating thepresence of the risk factor, (i) the icon representing the subjectvehicle, (ii) the icon representing the risk factor, and (iii) the iconrepresenting the direction in which the risk factor is present betweenthe icon representing the subject vehicle and the icon representing therisk factor.
 3. A driving assistance program product stored in anon-transitory storage medium and to be executed by a control unit of adriving assistance device, wherein the driving assistance deviceincludes a risk handling unit that executes a risk handling measureagainst an event threatening a safety of a driver when an occurrence ofthe event is predicted, the driving assistance program productcomprising instructions for implementing: obtaining a degree of a riskof the event threatening the safety of the driver when the occurrence ofthe event is predicted; obtaining a factor which causes the risk as arisk factor; and in response to determining that the risk handlingmeasure against the event that is predicted is not executed and thedegree of the risk is equal to or higher than a predetermined value,presenting, as information indicating a presence of the risk factor, (i)an icon representing the subject vehicle using a bird's eye view imagecaptured from a viewpoint positioned rear and above the subject vehicle,(ii) an icon representing the risk factor on front and lateral side ofthe icon representing the subject vehicle, and (iii) an iconrepresenting a direction in which the risk factor is present from aviewpoint of the subject vehicle between the icon representing thesubject vehicle and the icon representing the risk factor.
 4. A drivingassistance program product stored in a non-transitory storage medium andto be executed by a control unit of a driving assistance device, whereinthe driving assistance device includes a risk handling unit thatexecutes a risk handling measure against an event threatening a safetyof a driver when an occurrence of the event is predicted, the drivingassistance program product comprising instructions for implementing:obtaining a factor which causes the risk as a risk factor; and inresponse to determining that the risk handling measure against the eventthat is predicted is not executed and the risk factor exists,presenting, as information indicating a presence of the risk factor, (i)an icon representing the subject vehicle using a bird's eye view imagecaptured from a viewpoint positioned rear and above the subject vehicle,(ii) an icon representing the risk factor on front and lateral side ofthe icon representing the subject vehicle, and (iii) an iconrepresenting a direction in which the risk factor is present from aviewpoint of the subject vehicle between the icon representing thesubject vehicle and the icon representing the risk factor.